An efficient parallel computing simulation method based on OPenSeesMP considering local discontinuous domains

Abstract

The present invention discloses an efficient parallel computing simulation method based on OPenSeesMP considering local discontinuous domains. Aiming at the poor convergence of calculation iterations caused by the jump of grid size in the interaction between the site and the structure system in scientific research and practical engineering. In this paper, the near-field domain and the free-field domain of the structure-site interaction are divided with different grid sizes, and the weighted average method is used to interactively transfer data between the nodes in the far-field area and the calculation information in the near-field area, which can greatly shorten the calculation time, reduce the consumption of calculation resources, improve the calculation efficiency, and thus has a wide application prospect. The feasibility of the method is verified by carrying out large-scale shaking table tests on the liquefaction site-group pile foundation-superstructure system. In the three-dimensional finite element model, a non-liquefiable liquefaction constitutive model is adopted, the detachment and slip phenomena between the pile and the soil, and the pile cap and the soil are considered, and fiber materials are selected for the pile foundation to simulate the nonlinear deformation of concrete.

Description

Technical Field

[0001] The present invention relates to the technical field of seismic test simulation, and particularly relates to a method for simulating the interaction between a site and a structure system based on OPenSeesMP. Background Technique

[0002] For the liquefiable soil - pile foundation - superstructure system under cyclic dynamic loads, direct hazards such as foundation failure and coupled instability and failure of the superstructure caused by foundation liquefaction often occur. After soil liquefaction, the lateral constraint of the soil on the pile foundation is weakened, and liquefaction lateral spreading may occur. Many scholars have unanimously agreed through experiments and actual investigations that soil lateral spreading is one of the causes of pile foundation bending failure. At the same time, the influence of the inertial force of the superstructure needs to be considered. Such dynamic interaction between liquefied soil, pile foundation, and structure is actually a combined problem of the inertial effect of the superstructure and the motion effect of soil liquefaction lateral spreading.

[0003] In view of the limitations of model tests due to factors such as test sites, model conditions, costs, and labor, it is often impractical to conduct a large number of comprehensive experimental studies. The numerical analysis method of soil - structure dynamic interaction based on Biot's porous medium dynamic theory is a commonly used research method for the dynamic interaction problem of pile foundation - liquefied soil - superstructure, which can reflect the whole process of soil liquefaction and the failure mechanism of the structure. In the analysis process of the dynamic interaction between liquefied soil, pile foundation, and superstructure, various factors such as the dynamic properties of the site soil and the structure, the change of the mechanical properties of sandy soil after liquefaction, the deformation coordination of the soil - structure contact surface, and the transmission of soil - structure interaction forces need to be considered. Using traditional methods, the site - structure system needs to be divided into grids of the same size. When the structure system is relatively complex, it needs to be divided into extremely fine grids to complete the construction of structural grids, generating a huge number of elements and nodes. Ordinary computers cannot support its operation, and thus require huge computing resources to support the calculation, which affects its application in engineering and practice.

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide an efficient parallel computing simulation method based on OPenSeesMP considering local discontinuous domains, which can greatly shorten the computing time without reducing the computing accuracy. The following technical solutions are adopted:

[0005] An efficient parallel computing simulation method based on OPenSeesMP considering local discontinuous domains, comprising:

[0006] (1) Obtain the large - scale shaking table test site and structural monitoring data of the liquefiable site - group pile foundation - low - cap - superstructure system.

[0007] (2)According to the shaking table test plan, establish a dynamic interaction overall three-dimensional finite element model of the liquefied site - group pile foundation - low pile cap - superstructure system, and obtain the time history of the site and structural data, specifically including:

[0008] S1. Refer to the test plan design, and use the pre-processing software SKETCHUP to construct a dynamic interaction overall three-dimensional geometric model of the liquefied site - group pile foundation - low pile cap - superstructure system;

[0009] S2. Select an appropriate mesh element size, use the hexahedral structured mesh division method to divide the near-field area and free field area of the geometric model, and generate a parallel computing mesh according to the parallel requirements;

[0010] S3. Select the soil liquefaction constitutive model, unit material constitutive model, structure-site contact surface constitutive model, near-field area-free field area contact surface material

[0011] S4. Set appropriate boundaries and apply seismic excitation using an appropriate method;

[0012] S5. Draw contour maps of acceleration, velocity, displacement, pore pressure, etc. of the liquefied site - group pile foundation - low pile cap - superstructure system, extract the data information of the nodes at the same spatial positions in the test plan, and compare with the test detection data to verify the feasibility of this method.

[0013] Establishment of the three-dimensional geometric model of the site-structure system dynamic interaction in step S1:

[0014] S11. As a three-dimensional modeling software, SKETCHUP has powerful geometric modeling capabilities and can use tools such as points, lines, and planes in the software to establish various models. Refer to the large-scale shaking table test method to construct a dynamic interaction overall three-dimensional geometric model of the liquefied site - group pile foundation - low pile cap - superstructure system;

[0015] S12. During the process of establishing the geometric model, it is necessary to extract and divide the near-field area and free field area of the structural system into different solid geometries.

[0016] S13. During the process of establishing the geometric model, it is necessary to divide the geometric model into hexahedrons.

[0017] Generation of parallel computing mesh considering local discontinuous domains in step S2:

[0018] S21. According to the requirements of finite element calculation, the mesh size is less than 1 / 8 - 1 / 10 of the wavelength to obtain the minimum element size. In scientific research and engineering, the near-field domain of the structure is generally the focus of research and attention. Therefore, in order to obtain sufficient data, a relatively small mesh size is generally adopted in the near-field domain. To ensure the continuity of the mesh, the overall mesh size is generally small. Therefore, in this paper, the site is divided into the near-field domain and the far-field domain, and structural meshes are constructed using different element sizes.

[0019] S22. According to the parallel computing rules, the mesh of the liquefiable site - group pile foundation - low pile cap - superstructure system is divided into parallel computing meshes according to the requirements of the processor.

[0020] In step S3, consider the selection of site constitutive, structure, constitutive, element, etc.:

[0021] S31. The soil layer distribution in the large shaking table test is a 0.5-meter-thick dense sand layer at the bottom, a 1.2-meter-thick liquefiable loose sand layer in the middle, and a 0.3-meter-thick clay layer at the top.

[0022] S32. Pressure Independ MultiYield (PIMY) and Pressure DependMultiYield02 (PDMY02) are selected for clay and sand respectively. Among them, PIMY is not sensitive to the change of confining pressure, and PDMY02 is sensitive to the confining pressure;

[0023] S33. In order to save calculation time as much as possible, the soil layer solid element selects the 8-node hexahedron element of SSPbrickUP based on the U-P form of water-soil dynamic coupling considering the spatial pressure field. To reduce the physical stability necessary for integration, it includes an enhanced assumed strain field, and it has three translational degrees of freedom (u) in three directions and four degrees of freedom of pore water pressure (p).

[0024] S34. The pile foundation element selects the beam-column element based on force. Among them, Concrete02 material considering tensile strength is used for concrete, and Steel02 material with isotropic strain hardening is selected for steel bars;

[0025] S35. In order to be as close as possible to the actual situation of the test, the pile cap is adopted as the physical stable single-point integration hexahedron solid SSPbrick unit, and the superstructure is adopted as an elastic I-shaped section.

[0026] S36. The interaction between the soil and the structure is simulated using the frictional contact element ZeroLengthContactASDimplex based on the Mohr-Coulomb criterion developed by ASDEA Software Company. The contact between the structure and the site is established with the structure as the master node and the site as the slave node. The contact between the structure and the site is established through ZeroLengthContactASDimplex, and dynamic iterative calculations are performed by the Backward-Euler method.

[0027] S37. For the mesh generation and mapping establishment of the near-field domain of the structure and the far-field free-field domain, the free-field mesh is mapped to the near-field mesh using the weighted average, and data is transmitted in real time through the ASDEmbeddedNodeElement element and constrained by the penalty function.

[0028] In step S4, the selection of boundary and seismic excitation methods is considered:

[0029] S41. A one-way large laminar shear box is used in the test. The laminar shear box consists of a separation ring made of rectangular steel pipes. In addition, rolling bearings are set at the interfaces of adjacent frames and between the outer limiting frame and the laminated frame to form free-sliding fulcrums, so as to better realize the free shear deformation of the soil. In order to restore the test one-way layered shear box as much as possible, a shear beam boundary is adopted, so that the outer surface layer of the soil layer at the same height and the corner point of the left boundary are bound by the equalDOF command, so that the overall displacement of the outer surface layer of the soil layer is synchronized.

[0030] S42. In order to simulate the constraint of the limiting frame on the lateral deformation of the soil layer, the fix command is used to fix the lateral deformation of the outer boundary of the soil layer on the side of the limiting frame of the soil layer, and only the horizontal and longitudinal deformation of the soil layer is allowed;

[0031] S43. In order to make the simulation consistent with the test conditions, the pore pressure degrees of freedom at the bottom and both side boundaries of the model are constrained by the fix command to make them impermeable boundaries;

[0032] S44. The pore pressure degrees of freedom of the soil at the upper boundary of the three-dimensional model are not constrained, and the water level line is set on the surface of the clay layer;

[0033] The seismic wave time history collected on the tabletop is input at the bottom of the model using the method of uniform excitation. The measuring points at the same positions as those in the test in the dynamic interaction overall three-dimensional finite element model of the liquefaction site - group pile foundation - low pile cap - superstructure system are compared with the test results to verify the feasibility of this method.

[0034] Before applying the seismic wave load to the three-dimensional model, a quasi-static calculation of the site and the structure is also required to obtain the initial stress, initial displacement, etc. of the liquefaction site - group pile foundation - low pile cap - superstructure system:

[0035] Construct a finite element mesh considering local discontinuous domains, and perform a quasi-static analysis using a dynamic step with a step size of 10,000 to ensure sufficient drainage in the analysis, initial dynamic transient dissipation, initial excess pore pressure dissipation, and obtain the initial in-situ stress of the site.

[0036] The site-structure will exhibit nonlinearity under seismic excitation. To ensure that the soil undergoes irreversible plastic deformation under seismic excitation, the soil is adjusted from elastic to plastic using an extremely small time step to obtain the final initial in-situ stress of the site.

[0037] Load the structural system in the excavated site, and perform gravity loading on the structural system using the transient quasi-static method based on a relatively long time analysis step to ensure that the liquefied site - group pile foundation - low pile cap - superstructure system is in a quasi-static state before dynamic analysis.

[0038] Drawing of the contour map and extraction of the time history data of the detection points in step S5.

[0039] Draw contour maps of the acceleration, velocity, displacement, pore pressure, etc. of the liquefied site - group pile foundation - low pile cap - superstructure system, extract the data information of the nodes at the same spatial positions as in the test scheme, and compare it with the test detection data to verify the feasibility of this method.

[0040] Based on the OpenSeesMP software, the present invention proposes an efficient parallel computing simulation method for simulating local discontinuous domains of the site-structure system, and establishes a three-dimensional finite element model of the liquefied site - group pile foundation - low pile cap - superstructure system based on the large-scale shaking table test of the liquefied site - group pile foundation - low pile cap - superstructure system that has been carried out. Contacts between piles and soil, and between pile caps and soil are established. The plastic damage of the pile foundation is considered using fiber cross-sections. The test results are compared with the simulation results to verify the feasibility of this method. The results show that the calculated results of this model are in good agreement with the test results and can reflect the nonlinear dynamic response of the site-structure system.

[0041] The above description is only an overview of the technical solution of the present invention. In order to be able to more clearly understand the technical means of the present invention, it can be implemented in accordance with the content of the specification. And in order to make the above and other purposes, features and advantages of the present invention more obvious and understandable, the following specifically gives preferred embodiments and, in conjunction with the accompanying drawings, details are described as follows. Description of the Drawings

[0042] Figure 1 It is the plan view of the shaking table test.

[0043] Figure 2 It is the plan view of the layout of the test instruments.

[0044] Figure 3 It is the geometric model diagram.

[0045] Figure 4 is the site - structure system grid.

[0046] Figure 5 is the schematic diagram of non - continuous domain meshing.

[0047] Figure 6 The geometric longitudinal section of soil - pile - superstructure interaction used in numerical simulation.

[0048] Figure 7 is the fiber element of pile foundation.

[0049] Figure 8 is the pile - soil contact element.

[0050] Figure 9 is the cap - site contact element.

[0051] Figure 10 is the acceleration nephogram of liquefiable site - group pile foundation - low - cap - superstructure system.

[0052] Figure 11 is the velocity nephogram of liquefiable site - group pile foundation - low - cap - superstructure system.

[0053] Figure 12 is the displacement nephogram of liquefiable site - group pile foundation - low - cap - superstructure system.

[0054] Figure 13 is the pore - pressure nephogram of liquefiable site - group pile foundation - low - cap - superstructure system.

[0055] Figure 14 is the comparison diagram of test and simulation of excess pore - pressure ratio time - history curve in liquefiable site.

[0056] Figure 15 is the comparison diagram of test and simulation of acceleration time - history curve in liquefiable site.

[0057] Figure 16 is the comparison diagram of test and simulation of moment time - history curve of liquefiable site - group pile foundation - low - cap - superstructure system. Detailed implementation manners

[0058] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments given are not intended to limit the present invention.

[0059] The liquefiable sloping site - group pile foundation - superstructure system simulated in the embodiment was completed by Pengfei Dou et al. The layout of the test structure is as Figure 1As shown in the figure, the soil layers of the model foundation from bottom to top consist of a 0.5m thick dense sand layer, a 1.2m thick liquefiable saturated sand layer, and a 0.3m thick clay covering layer. The fabrication method of the two groups of test model foundations is as follows: For the bottom dense sand layer, a method combining layered ramming and static pressure is adopted, with a virtual paving thickness of 250mm for each layer. According to the actual situation, various construction methods such as vibration, pressing, and ramming are used to ensure the compactness of the model soil. After that, water is introduced into the model box through a water pipe until it exceeds the top of the sand layer by 20cm, and after standing for 2h, the liquefiable saturated sand layer is prepared. The liquefiable sand layer is prepared by an improved water sedimentation method. A certain height of water is introduced into the model box, and fine sand is evenly scattered into the water by the way of sand lifting, always keeping the water surface about 10cm higher than the sand sample surface. After the preparation of the liquefiable sand layer is completed, it is left standing for 6h, and a 30cm thick clay layer is laid on the surface of the sand as the covering layer. After standing for a certain period of time, the natural consolidation process of the soil body is simulated.

[0060] The model pile foundation is a 2×2 group pile foundation composed of 4 piles embedded in the pile cap. Its dimensions are: pile length 1700mm, pile body diameter 100mm, and the length extending into the dense sand layer is 400mm (4 times the pile diameter). The length of the pile foundation embedded in the pile cap is 50mm. The dimensions of the model pile cap are: length 800mm, width 800mm, and height 250mm. The materials of the pile foundation model mainly consist of micro-concrete, steel bars, and galvanized wire meshes. Micro-concrete is a kind of model concrete, using larger-sized gravel as coarse aggregate and smaller-sized gravel as fine aggregate. Since the construction method, vibration mode, curing conditions, and material properties of micro-concrete are very similar to those of ordinary concrete, it has a good similarity relationship with the prototype concrete in dynamic characteristics, and by adjusting the mix ratio, the requirement of reducing the elastic modulus can be met. In this series of tests, the model pile foundation is made of micro-concrete, and the mix ratio adopted is water:cement:lime:coarse sand = 0.5:1:0.58:5. The selected compressive strength of the micro-concrete test block (7.07cm×7.07cm×7.07cm cube test block) is 17.1Mpa, and its elastic modulus (10cm×10cm×30cm prism test block) is 15340Mpa. Since the pile cap is the link between the pile foundation and the above-ground structure, and stress concentration is likely to occur at the pile cap part, the pile cap adopts a reinforced concrete structure. The top of the pile foundation is embedded in the pile cap, and the embedded depth is 50mm. The upper structure is a two-story lumped mass model with a height of 3 meters, and each layer has a counterweight of 410kg.

[0061] Refer to Figure 2, Sensor layout diagram. The signals to be measured in the experiment include: strain (bending moment) of the pile shaft, acceleration responses of the pile cap and the superstructure, acceleration response of the foundation soil, displacements of the pile shaft, soil, and superstructure, settlement of the foundation soil, dynamic earth pressure, pore water pressure, etc. For the signals to be tested, the main sensor devices to be used are: strain gauges, acceleration sensors, waterproof accelerometers, array displacement gauges (SAA), laser displacement sensors, miniature earth pressure cells, and miniature pore water pressure sensors. Different acceleration sensors are used at different positions for testing acceleration signals: miniature accelerometers are mainly used on the superstructure and the pile cap, and are pasted on the surface of the structure; waterproof accelerometers (A1 - A6) are used in the liquefiable foundation, mainly for the foundation soil; in addition, the acceleration sensors in the array displacement gauge SAA can be used for testing the acceleration of the pile shaft and the foundation soil. According to the static and dynamic pressure estimations, a full scale of 20 KPa or 30 KPa can be used in the shallow foundation

[0062] (1) Obtain the large - scale shaking table test free - field, near - field, and structural monitoring data of the liquefiable site - pile group foundation - low - pile - cap - superstructure system.

[0063] (2) According to the shaking table test plan, establish a dynamic interaction overall three - dimensional finite element model of the liquefiable site - pile group foundation - low - pile - cap - superstructure system, and obtain the time - history of the site and structural data, specifically including:

[0064] Establishment of the three - dimensional geometric model of the site - structure system dynamic interaction in step S1:

[0065] S11. Refer to Figure 3 the geometric model diagram, SketchUp. As a three - dimensional modeling software, it has powerful geometric modeling capabilities and can use tools such as points, lines, and planes in the software to establish various models. Refer to the large - scale shaking table test method to construct the overall three - dimensional geometric model of the dynamic interaction of the liquefiable site - pile group foundation - low - pile - cap - superstructure system;

[0066] S12. During the establishment of the geometric model, it is necessary to extract and divide the near - field and free - field of the structural system into different solid geometries.

[0067] S13. During the establishment of the geometric model, it is necessary to divide the geometric model into hexahedrons.

[0068] Generation of parallel computing grids considering local discontinuous domains in step S2:

[0069] S21. Refer to Figure 4, Liquefaction site - group pile foundation - low pile cap - upper structure system grid diagram. According to the finite element calculation requirements, the grid size is less than 1 / 8 - 1 / 10 of the wavelength to obtain the minimum element size. In scientific research and engineering, the near - field area of the structure is generally the focus of research and attention. Therefore, in order to obtain sufficient data, a smaller grid size is generally used in the near - field area. To ensure the continuity of the grid, the overall grid size is generally small. Therefore, in this paper, the site is divided into a near - field area and a far - field area, and structural grids are constructed using different element sizes, with the near - field area refined. Under the requirement of meeting the calculation accuracy, a larger grid element size is used as much as possible in the free - field area to save computing resources.

[0070] S22, Refer to Figure 5 , According to the parallel computing rules, considering the computing resources and computing efficiency of the server comprehensively, the liquefaction site - group pile foundation - low pile cap - upper structure system grid is divided into parallel computing grids according to the parallel computing requirements.

[0071] Selection of site constitutive, structure, constitutive, element, etc. in step S3:

[0072] S31. The soil layer distribution of the large - scale shaking table test is a 0.5 - meter - thick dense sand layer at the bottom, a 1.2 - meter - thick liquefiable loose sand layer in the middle, and a 0.3 - meter - thick clay layer at the top.

[0073] S32. Refer to Figure 6 , In the numerical simulation of the geometric longitudinal section of the bridge - foundation coupling system, Pressure Independ MultiYield (PIMY) and Pressure DependMultiYield02 (PDMY02) are selected for clay and sand respectively. Among them, PIMY is not sensitive to the change of confining pressure, and PDMY02 is sensitive to the confining pressure;

[0074] S33. In order to save computing time as much as possible, the soil layer solid element selects the 8 - node hexahedron element of SSPbrickUP based on the U - P form of water - soil dynamic coupling considering the spatial pressure field, which has three - direction translational degrees of freedom (u) and four degrees of freedom of pore water pressure (p) to reduce the physical stability necessary for integration, including the enhanced assumed strain field.

[0075] S34. Refer to Figure 7 , For the fiber cross - section of the pile foundation, the pile foundation element selects the beam - column element based on force. Among them, Concrete02 material considering tensile strength is used for concrete, and Steel02 material with isotropic strain hardening is selected for steel bars;

[0076] S35. In order to be as close as possible to the actual situation of the test, the pile cap is adopted with the physical stable single - point integration hexahedron solid SSPbrick element, and the upper structure is adopted with an elastic I - type cross - section.

[0077] S36, Refer to Figure 8 , for the pile-soil contact surface, the interaction between the soil and the structure is simulated using the ZeroLengthContactASDimplex friction contact element based on the Mohr-Coulomb criterion developed by ASDEA Software Company. To establish the contact between the structure and the site, the pile foundation is taken as the master node and the soil as the slave node. The contact between the structure and the site is established through ZeroLengthContactASDimplex, and dynamic iterative calculations are carried out by the Backward-Euler method;

[0078] S37, Refer to Figure 9 , for the cap-soil contact surface, taking the cap as the master node and the soil as the slave node, the contact between the cap and the soil is simulated using the BeamContact3D material on the OpenSee official website to simulate the soil-structure interaction, and the Lagrange multiplier is used for constraint.

[0079] S38, For the mesh generation and mapping establishment between the near-field domain of the structure and the far-field free-field domain, the free-field mesh is mapped to the near-field mesh using the weighted average, and data is transmitted in real time through the ASDEmbeddedNodeElement unit material, and constraints are imposed through the penalty function.

[0080] In step S4, the selection of boundary and seismic excitation method is considered:

[0081] S41, The test uses a one-way large laminar shear box, which consists of a separation ring made of rectangular steel pipes. In addition, rolling bearings are set at the interfaces of adjacent frames and between the outer restraint frame and the laminated frame to form free-sliding fulcrums, so as to better realize the free shear deformation of the soil. In order to restore the test one-way layered shear box as much as possible, a shear beam boundary is adopted, so that the outer surface layer and the left boundary corner point at the same height of the soil layer are bound by the equalDOF command, so that the overall displacement of the outer surface layer soil of the soil layer is synchronized.

[0082] S42, In order to simulate the constraint of the restraint frame on the lateral deformation of the soil layer, the fix command is used to fix the lateral deformation of the outer boundary of the soil layer on the side of the restraint frame of the soil layer, and only the horizontal and longitudinal deformation of the soil layer is allowed;

[0083] S43, In order to make the simulation consistent with the test conditions, the pore pressure degrees of freedom at the bottom and both side boundaries of the model are constrained by the fix command to make it an impermeable boundary;

[0084] S44, The pore pressure degrees of freedom of the soil at the upper boundary of the three-dimensional model are not constrained, and the water level line is set on the surface of the clay layer;

[0085] S45. Input the seismic wave time history collected from the tabletop into the bottom of the model by the method of uniform excitation, and compare the measuring points at the same positions in the dynamic interaction overall three-dimensional finite element model of the liquefied site - group pile foundation - low pile cap - superstructure system with the test results to verify the feasibility of this method.

[0086] The drawing of the nephogram and the extraction of the time history data of the detection points in step S5;

[0087] Refer to Figure 10 , the acceleration nephogram of the liquefied site - group pile foundation - low pile cap - superstructure system. It can be seen from the figure that the acceleration in the near-field free field can transition well and there is no jump in the nephogram, verifying the feasibility of this method;

[0088] Refer to Figure 11 , the velocity nephogram of the liquefied site - group pile foundation - low pile cap - superstructure system. It can be seen from the figure that the velocity in the near-field free field can transition well and there is no jump in the nephogram, verifying that this method can implement the velocity data transfer well;

[0089] Refer to Figure 12 , the displacement nephogram of the liquefied site - group pile foundation - low pile cap - superstructure system. It can be seen from the figure that the displacement in the near-field free field can transition well and there is no jump in the nephogram, verifying the feasibility of this method;

[0090] Refer to Figure 13 , the pore pressure nephogram of the liquefied site - group pile foundation - low pile cap - superstructure system. It can be seen from the figure that the pore pressure in the near-field free field can transition well and there is no jump in the pore pressure nephogram, verifying the feasibility of this method;

[0091] Refer to Figure 14Comparison diagram of the time history curves of excess pore pressure ratios in the far and near fields of a loose sand site, showing good agreement between the experimental and numerical solutions of excess pore pressure at each measuring point. The variation trends of the pore pressure time history curves are basically the same, and the occurrence times of the curve peaks are also basically consistent. According to the entire process of excess pore pressure development in the figure and the corresponding seismic input acceleration time history, the excess pore pressure time history curves of each measuring point are divided into five stages: stage I of non-developed excess pore pressure, stage II of rapid formation of excess pore pressure during the main shock, stage III of liquefaction during the main shock, stage IV of continuous liquefaction during aftershocks, and stage V of dissipation of excess pore pressure. In stage II, as the main shock acceleration amplitude of the Wolong wave increases, pore pressure accumulates rapidly, and the excess pore pressure time history curves of each measuring point rise rapidly, approaching the initial vertical effective stress. However, at this time, the acceleration of the main shock has not reached its peak. In stage III, when the main shock acceleration reaches its peak, the excess pore pressure at each measuring point increases to the maximum value, equal to the initial vertical effective stress, and the soil is completely liquefied at this time. As the main shock acceleration decreases, the excess pore pressure at the deep measuring points decreases slightly, indicating that pore water drains upward and soil particles are redistributed. In stage IV, when the acceleration amplitude increases again during aftershocks, it is obvious that the excess pore pressure at each measuring point shows a peak again, equal to the initial effective stress, indicating that aftershocks may cause secondary liquefaction of the soil or maintain the liquefied state of the soil. In stage V, as the amplitude of the input ground motion acceleration weakens, the excess pore pressure at the deep and middle measuring points begins to decrease slowly, the soil pores are redistributed and gradually tend to a stable state. For the shallow measuring points, the excess pore pressure always equals the initial vertical effective stress. This is because there is a clay layer with extremely low permeability overlying the loose sand layer. Although pore water dissipates upward, the clay layer can be regarded as an approximately impermeable boundary that blocks the drainage of pore water, and pore water gradually accumulates at the interface between the non-liquefied clay layer and the loose sand layer, resulting in the sand near this area being basically in a liquefied state all the time.

[0092] The development trends of pore pressure at far-field and near-pile measuring points are compared. There are obvious small fluctuations in the excess pore pressure at the near-pile measuring points during the main shock and aftershock stages (stages III and IV), indicating that soil dilation occurs. Soil dilation may be due to the detachment and slip between the structure and the soil during vibration, resulting in gaps at the soil-structure interface, providing a dissipation channel for pore pressure. It may also be due to the presence of the pile foundation, which hinders the flow of pore water, causing pore water to diffuse and flow towards the soil around the pile foundation, thereby causing the soil around the pile to expand.

[0093] Refer to Figure 15Comparison diagram of acceleration time history curve test and data simulation. By comparing the acceleration time history of the test solution and the numerical solution, the numerical results of the acceleration time history curve at the middle and deep measuring points in the soil layer are in good agreement with the test results. As the soil depth decreases, the acceleration amplification factor at each measuring point shows a trend of first decreasing and then increasing. The acceleration peak value at the dense sand layer measuring point is the largest. The reduction amplitude of the reaction acceleration at the middle measuring point of the loose sand layer is the most obvious, and it increases at the upper part of the loose sand layer and the clay layer measuring points. It can be seen that the acceleration peak value of the soil at the pile tip is the largest, and the acceleration amplification factor of the loose sand layer decays to 50% of the seismic input. Since the loose sand layer has been in a liquefied state after the development of excess pore pressure, the seismic energy is significantly dissipated in the soil, indicating that soil softening (after liquefaction) has the effect of reducing the acceleration amplitude.

[0094] Figure 16 For the comparison diagram of the moment time history curve test and data simulation, the comparison results of the test and numerical moments at each point of the pile foundation are basically in agreement, and except for the pile head and pile tip, the amplitudes of the moments at other measuring points are also basically the same. The lateral displacement of the site soil is the main factor causing the residual moment of the pile foundation. For the model displacement time history, when the seismic record input ends, the liquefaction of the foundation soil weakens the constraint of the soil on the pile foundation, resulting in a decrease in the lateral displacement amplitude of the pile foundation after the foundation soil liquefies. Therefore, no obvious residual moment appears at each point of the pile foundation. The embedding method of the test pile foundation is not completely consolidated, and there is a residual moment at the pile head; the pile tip is not fixed and is in the form of a free end. The amplitude of the numerical solution of the moment at the adjacent node (1.7 m) above the pile tip is larger than the test solution. The yield curvature of the concrete pile foundation section analysis is 0.03 rad / m, and the corresponding yield moment is 2258 N*m. By comparison, it can be seen that the moment amplitudes at each section of the pile foundation are very small, indicating that the pile is basically in a linear elastic state during the test and no obvious nonlinear reaction occurs.

[0095] Based on the OpenSeesMP software, the present invention proposes an efficient parallel computational simulation method for simulating the local discontinuous domain of the site-structure system, and establishes a three-dimensional finite element model of the liquefied site-group pile foundation-low pile cap-upper structure system based on the large-scale shaking table test of the liquefied site-group pile foundation-low pile cap-upper structure system that has been carried out. The contact between the pile and the soil, and the pile cap and the soil is established. The fiber section is used to consider the plastic damage of the pile foundation. The test results are compared with the simulation results to verify the feasibility of the method. The results prove that the calculation results of this model are in good agreement with the test results and can simulate the nonlinear dynamic response of the site-structure system.

Claims

1. An efficient parallel computing simulation method based on OPenSeesMP considering local discontinuous domains, characterized in that Including: (1) Obtain the large-scale shaking table test site and structural monitoring data of the liquefied site - group pile foundation - low pile cap - superstructure system; (2) According to the shaking table test plan, establish a dynamic interaction overall three-dimensional finite element model of the liquefied site - group pile foundation - low pile cap - superstructure system, and obtain the time history of site and structural data, specifically including: S1. Refer to the test plan design, and use the preprocessing software SKETCHUP software to construct a dynamic interaction overall three-dimensional geometric model of the liquefied site - group pile foundation - low pile cap - superstructure system; S2. Select the mesh element size, use the hexahedron structured mesh division method to divide the near-field area and free field area of the geometric model, and generate a parallel computing mesh according to the parallel requirements; S3. Select the soil liquefaction constitutive model, unit material constitutive model, structure-site contact surface constitutive model, near-field area-free field area contact surface material; S4. Set appropriate boundaries and apply seismic excitation by an appropriate method; S5. Draw the acceleration, velocity, displacement, and pore pressure nephograms of the liquefied site - group pile foundation - low pile cap - superstructure system, extract the data information of the nodes at the same spatial positions in the test plan, and compare it with the test detection data to verify the feasibility of this method; Consider the selection of boundaries and seismic excitation methods in step S4: S41. In the test, a one-way large-scale laminar shear box is used, and the laminar shear box consists of a separation ring made of rectangular steel pipes; in addition, rolling bearings are set at the interfaces of adjacent frames and between the external restraint frame and the laminated frame to form free sliding supports, so as to realize the free shear deformation of the soil; the shear beam boundary is adopted, so that the outer surface layer and the left boundary corner point at the same height of the soil layer are bound by the equalDOF command to make the overall displacement of the outer surface layer soil of the soil layer synchronous; S42. Simulate the constraint of the lateral deformation of the soil layer by the restraint frame, and use the fix command to fix the lateral deformation of the outer boundary of the soil layer on the side of the soil layer restraint frame, and only allow the horizontal and longitudinal deformation of the soil layer; S43. To make the simulation consistent with the test conditions, the pore pressure degrees of freedom at the bottom and both side boundaries of the model are constrained by the fix command to make it an impermeable boundary; S44. Do not constrain the pore pressure degrees of freedom of the soil on the upper boundary of the three-dimensional geometric model, and set the water level line on the surface of the clay layer; S44. Input the seismic wave time history collected by the table top into the bottom of the model by the method of uniform excitation, and compare the measuring points at the same positions in the liquefied site - group pile foundation - low pile cap - superstructure system dynamic interaction overall three-dimensional finite element model with the test results to verify the feasibility of this method; Before loading the seismic wave load on the three-dimensional finite element model, it is also necessary to perform the quasi-static calculation of the site and the structure to obtain the initial stress and initial displacement of the liquefied site - group pile foundation - low pile cap - superstructure system: Construct a finite element mesh considering the local discontinuous domain, and use a dynamic step with a step size of 10000 for quasi-static analysis to ensure sufficient drainage in the analysis, initial dynamic transient dissipation, initial excess pore pressure dissipation, and obtain the initial stress of the site; The site-structure will exhibit nonlinearity under seismic excitation. To ensure that the soil undergoes irrecoverable plastic deformation under seismic excitation, a very small time step is used to adjust the soil from elastic to plastic, and the final initial site stress is obtained. In the excavated site, the structural system is loaded. The transient pseudo-static method is used to perform gravity loading on the structural system based on a relatively long time analysis step to ensure that the liquefied site-pile group foundation-low pile cap-upper structure system is in a pseudo-static state before dynamic analysis.

2. An efficient parallel computing simulation method based on OPenSeesMP considering local discontinuous domains according to claim 1, characterized in that Drawing of the nephogram and extraction of the time history data of the detection points in step S5; Draw the acceleration, velocity, displacement, and pore pressure nephograms of the liquefied site-pile group foundation-low pile cap-upper structure system, extract the data information of the nodes at the same spatial positions as in the test scheme, and compare it with the test detection data to verify the feasibility of this method.

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